With floor-bound vehicles, in particular automated guided vehicles, there is an increasing need to monitor the route of the vehicle for the presence of obstacles by means of suitable sensors. Laser scanners are frequently used for this purpose. Such laser scanners as a rule have movable optics and apparatus for measuring the time of flight, which is associated with high costs.
An alternative to the use of laser scanners comprises the use of monitoring sensors in accordance with the initially named kind working in accordance with the principle of laser triangulation.
The distance of an object or obstacle present in the monitored zone can be determined with the aid of such a monitoring sensor. The light generated by the light source of the light transmitter is focused with the aid of the transmission optics to form a transmitted light beam that is incident in the monitored zone on an object to be detected that may be located there. The transmitted light can be remitted, i.e. diffusely or specularly reflected, by such an object. It passes through a reception optics and can be detected by a light receiver that forms a reception unit together with the reception optics. The light receiver comprises an array of photosensitive receiver elements in known solutions.
The position of a light spot generated by the remitted light on the light receiver in the so-called direction of triangulation changes in dependence on the distance between the monitoring sensor and the remitting object. There is a clear geometrical relationship between the point of incidence on the light receiver and the distance of the detected object. The distance between the object and the monitoring sensor can thus be determined by evaluating the light distribution on the light receiver.
A monitoring sensor can be mounted at a vehicle for monitoring the route, with the monitoring sensor expediently being arranged spaced apart from the route to be monitored and being aligned such that the transmitted light is emitted obliquely at a predefined angle of inclination in the direction of the route and is incident there at a corresponding spacing from the monitored sensor. The route thus represents a scanning plane. The monitored zone extends between the monitoring sensor and the place of incidence of the transmitted light on the scanning plane.
If the transmitted light is incident on an object in the monitored zone that is located closer to the monitoring sensor than the place of incidence of the transmitted light on the scanning plane, the transmitted light that passes through the reception optics is remitted at a different angle in the direction of the reception optics so that the position of the light spot generated from the remitted light is displaced in the direction of triangulation on the light receiver.
So that not only objects can be detected that are located directly in the line of sight of the monitoring sensor, i.e. on or close to the optical axis of the transmission optics, the transmitted light can be laterally widened so that it generates a scanning light line that extends transversely to the line of sight of the monitoring sensor and thus as a rule transversely to the direction of locomotion of the vehicle and in parallel with the scanning plane on the incidence on the scanning plane or generally on an imaginary projection surface.
The transmitted light is so-to-say widened in fan shape so that the monitored zone extends in sector form from the monitoring sensor. The light transmitter, the light receiver, and the reception optics are usually adapted and aligned such that the scanning light line extends as a straight line on the scanning plane transversely to the main monitoring direction of the monitoring sensor, said straight line being imaged as a straight-line light spot on the light receiver in the absence of obstacles, with said straight-line imaging extending in parallel with the rows or columns of the light receiver in which the receiver elements are arranged.
A lateral position on the light receiver, i.e. position in the direction of extent of the linearly imaged light spot here corresponds to a respective angular position within the sector-shaped monitored zone.
If an object is located within the monitored zone that is detected by the transmitted light, the place of incidence of the light received from the corresponding angle is displaced transversely, in particular perpendicular, to the direction of extent of the light spot on the light receiver. In other words, a short segment of the linear received light spot whose length depends on the angular range over which the detected object extends is displaced transversely to the direction of extent of that straight-line received light spot that would be generated without the presence of objects in the monitored zone.
Objects that are located outside a main direction of monitoring extending in the direction of the optical axis of the transmission optics can, however, not be detected sufficiently reliably and early enough by such a monitoring sensor. The main monitoring direction coincides as a rule with the direction of locomotion of a vehicle carrying the monitoring sensor.
There is a need also to detect such external vehicles or other obstacles that move transversely to this direction of locomotion and that could intersect the route of the vehicle with a risk of collision.